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The term temperature sensor refers to a class of devices that provide a measurement of the temperature of objects, and either display a reading directly or produce an output signal whose value can be translated into a temperature reading. Temperature is a fundamental measurement of thermal energy and can be thought of as a measure of the average kinetic energy of the atoms and molecules of a material.

There are several types of temperature sensors used in industrial applications. This article will review the different types of temperature sensors and provide information on how they function and their applications. To learn more about other sensors, review our related article Sensors – A Complete Guide (Types, Applications, and Suppliers).

Temperature sensor types
Temperature sensors generally fall into one of these primary types:

  • Thermocouples
  • RTDs (Resistance Temperature Detectors)
  • Thermistor Temperature Sensors
  • Semiconductor Temperature Sensors
  • Thermometers
  • Vibrating Wire Temperature Sensors

The majority of these (the exception being infrared temperature sensors) are contact sensors, meaning that the sensor or probe must physically contact the object whose temperature is being measured in order to take a reading. Infrared sensors measure the radiated thermal energy from the object to establish its temperature and therefore are non-contact sensors.

With the exception of some forms of thermometers, most temperature sensors are designed to generate an electrical signal output that is used to establish the value of temperature.

Thermocouples
Thermocouples measure temperature by making use of a probe constructed by joining two different metals together to form a junction at one end and to which a voltmeter is connected at the other end. The end of the probe called the hot junction (where the metals are joined) is used to contact the object whose temperature is being measured, while the other end of the probe called the cold junction is sitting at a reference temperature. A potential difference in Volts recorded on the voltmeter will be present whose value proportionally represents the temperature difference between the hot and cold junctions of the thermocouple.

Most thermocouples are covered in a protective sheath to isolate the metals from the ambient temperature and to provide some degree of protection against corrosion. Sheath materials include 1316 stainless steel, 304 stainless steel, or Inconel 600 as examples.

Depending on the specific metals used to fabricate the thermocouple, the devices are assigned a letter type such as Type J, K, T, N, E, B, R, or S. Each of these types has specific characteristics relating to its temperature range, vibration resistance, chemical compatibility, and applications. Base metal thermocouples are types J, K, T, & E, and are the most common. So-called Noble metal thermocouples are types R, S, and B. Table 1 below lists the various types of thermocouples and their metal composition.

Read more: All About Temperature Sensors